Communication server apparatus using frequency multiplexing and method

ABSTRACT

A communication server ( 58 ) includes a plurality of pairs of frequency agile modulators ( 638 ) and demodulators ( 640 ) each set to operate at a unique frequency and associated with a twisted pair data line ( 54 ). The communication server ( 58 ) also includes a plurality of pairs of demodulators ( 644 ) and modulators ( 646 ) that each have a designatable operation frequency and are associated with one of a plurality of XDSL modems ( 648 ). A mixer ( 642 ) operates to combine signals from the frequency agile modulators ( 638 ) and provide the combined signal to the demodulators ( 644 ). The mixer ( 642 ) further operates to combine signals from the modulators ( 646 ) and provide the combined signal to the frequency agile demodulators ( 640 ). A detector ( 634 ) operates to detect a need for data service on a selected twisted pair data line ( 54 ). The controller ( 636 ) then operates to couple the selected twisted pair data line ( 54 ) to the selected XDSL modem ( 648 ) by designating the demodulator ( 644 ) and modulator ( 646 ) pair associated with the selected XDSL modem ( 648 ) to operate at the unique frequency of the frequency agile modulator ( 638 ) and demodulator ( 640 ) associated with the selected twisted pair data line ( 54 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.08/781,482, filed Jan. 10, 1997 by John F. McHale, James R. Sisk, RobertH. Locklear, Jr., Jason McCullough, Clifford L. Hall and Ronald E. Hamentitled “Communication Server Apparatus Using Frequency Multiplexingand Method,” pending; which is a continuation-in-part of U.S. patentapplication Ser. No. 08/625,769, filed Mar. 29, 1996 by John F. McHaleentitled “Communication Server Apparatus and Method,” pending.

This application is related to: U.S. patent application Ser. No.08/781,444, filed Jan. 10, 1997, and entitled “Communication ServerApparatus Having Four-Wire Switching Interface and Method,” now pending;U.S. patent application Ser. No. 08/781,450, filed Jan. 10, 1997, andentitled “Communication Server Apparatus Using Digital Signal Switchingand Method,” now U.S. Pat. No. 5,898,761; and U.S. patent applicationSer. No. 08/781,441, filed Jan. 10, 1997, and entitled “CommunicationServer Apparatus Having Distributed Switching and Method,” now U.S. Pat.No. 5,852,655.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to data communication, and moreparticularly to a communication server apparatus using frequencymultiplexing and method.

BACKGROUND OF THE INVENTION

A communication server provides access to communication facilities. Forexample, a communication server having a bank of modems may providesubscriber access to the modems for data communication. A communicationserver may be associated with its own dedicated communication network,or with an existing communication network, such as the public switchedtelephone network (PSTN).

As communication networks provide greater connectivity and access toinformation, there is an increasing demand for data communication athigher rates. One solution to provide increased data rates replacesexisting twisted pair wiring with high bandwidth media, such as coaxialcables or fiber optic links. Other solutions adopt improvedcommunication techniques using the existing hardware infrastructure. Forexample, digital subscriber line (XDSL) technology provides higherbandwidth data service over existing twisted pair wiring.

To deliver data service to the subscriber, a communication server mayprovide a dedicated or permanent connection to its communicationfacilities. For example, an existing communication server at a centraloffice provides enough communication facilities to simultaneouslyservice all PSTN subscribers. However, all telephone subscribers may notdesire data service. Furthermore, the subscribers that desire dataservice may not simultaneously access the communication server.

SUMMARY OF THE INVENTION

In accordance with the present invention, the disadvantages and problemsassociated with communication servers have been substantially reduced oreliminated. In particular, a communication server apparatus usingfrequency multiplexing and method are disclosed that provide dataservice to a number of subscribers using a reduced number of XDSLcommunication facilities.

In accordance with one aspect of the present invention, a communicationserver includes a plurality of pairs of receiver/buffers andtransmit/buffers coupled to associated twisted pair data lines. Thecommunication server also includes a plurality of pairs of frequencyagile modulators and demodulators. Each frequency agile modulator anddemodulator pair is coupled to an associated receiver/buffer andtransmit/buffer pair and is set to operate at a unique frequency. Thecommunication server further includes a plurality of pairs ofdemodulators and modulators. Each demodulator and modulator pair has adesignatable operation frequency. A plurality of XDSL modems are eachcoupled to an associated demodulator and modulator pair. A mixer iscoupled to the pairs of frequency agile modulators and demodulators andcoupled to the pairs of demodulators and modulators. The mixer operatesto combine signals from the frequency agile modulators and provide thecombined signal to the demodulators. The mixer further operates tocombine signals from the modulators and provide the combined signal tothe frequency agile demodulators. The communication server includes adetector that operates to detect a need for data service on a selectedtwisted pair data line. A controller is coupled to the detector and tothe pairs of demodulators and modulators. The controller operates toselect one of the XDSL modems in response to detecting the need for dataservice. The controller further operates to couple the selected twistedpair data line to the selected XDSL modem by designating the demodulatorand modulator pair associated with the selected XDSL modem to operate atthe unique frequency of the frequency agile modulator and demodulatorassociated with the selected twisted pair data line.

According to another aspect of the present invention, a method isprovided for coupling a selected subset of a plurality of twisted pairsubscriber lines to a plurality of XDSL modems. Each twisted pairsubscriber line is split into a twisted pair data line and a twistedpair phone line. For each twisted pair data line, signals received onthe twisted pair data line are modulated at a unique frequencyassociated with the twisted pair data line. The modulated receivedsignals are mixed to produce a combined incoming signal. For each XDSLmodem, the combined incoming signal is demodulated at a designatedfrequency associated with the XDSL modem and outgoing signals aremodulated at the designated frequency. The modulated outgoing signalsare mixed to produce a combined outgoing signal. For each twisted pairdata line, the combined outgoing signal is demodulated at the uniquefrequency associated with the twisted pair data line to recover signalsfor transmission on the twisted pair data line. A need for data serviceis detected on a selected twisted pair data line, and one of the XDSLmodems is selected in response to detecting the need for data service.The selected XDSL modem is then coupled to the selected twisted pairdata line by setting the designated frequency associated with the XDSLmodem to the unique frequency associated with the selected twisted pairdata line.

An important technical advantage of the present invention is thatfrequency multiplexing can be beneficial to a communication serverlocated at a cable operator.

Another important technical advantage of the present invention is thedistribution of the switching function to allow scalability of thenumber of supported data lines and over-subscription of XDSL modems.

Important technical advantages of the present invention include acommunication server that provides data service to a number ofsubscribers using a reduced number of XDSL communication facilities.Over-subscription of data service is accomplished by selectivelycoupling a number of twisted pair data lines to a reduced number of XDSLmodems. A controller polls the data lines in succession to determinewhich subscribers of the communication system need data service. Upondetecting a need for data service on a selected data line, thecontroller directs a switch to couple the selected data line to anavailable modem. The communication server may then provide data servicesuitable for high bandwidth applications, such as video-on-demand,multimedia, or Internet access.

Another important technical advantage of the present invention includesa communication server that provides over-subscribed XDSL data serviceusing the existing infrastructure of the public switched telephonenetwork (PSTN). Asymmetric digital subscriber line (ADSL), symmetricdigital subscriber line (SDSL), high-speed digital subscriber line(HDSL), very high-speed digital subscriber line (VDSL), or othersuitable XDSL technology can provide higher bandwidth data service overexisting twisted pair wiring. These technologies may support dataservice simultaneously with traditional telephone service using aseparation technique, such as frequency division multiplexing. In oneembodiment, a splitter divides each incoming twisted pair subscriberline into a twisted pair phone line and a twisted pair data line. Thephone line is coupled to a telephone switch to provide telephone serviceand the data line is coupled to the communication server to provideover-subscribed XDSL data service. The communication server and splittermay be located at a central office of the PSTN.

Another important technical advantage of the present invention includesthe management and monitoring of XDSL data service provided tosubscribers. To accomplish this, the communication server maintains anactivity table to determine status information on twisted pair datalines and XDSL modems. In addition, the communication server can tracksubscriber usage, monitor subscriber information and generate billingand demographic information. In a particular embodiment, an activitydetector disconnects a subscriber after a predetermined period ofinactivity to release a modem for use by another subscriber.

An additional important technical advantage of the present inventionincludes switching the connections between data lines and the XDSL⁵modems using frequency modulation and mixing. Other important technicaladvantages are readily apparent to one skilled in the art from thefollowing figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and forfurther features and advantages, reference is now made to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a communication system that provides telephone anddata service;

FIG. 2 illustrates a communication server in the communication system;

FIG. 3 illustrates in more detail the controller of the communicationserver;

FIG. 4 illustrates in more detail the switch and modem pool of thecommunication server;

FIG. 5 illustrates in more detail the transceiver in the controller ofthe communication server;

FIG. 6 illustrates in more detail the detector in the controller of thecommunication server;

FIG. 7 illustrates an activity table used by the controller of thecommunication server;

FIG. 8 is a flow chart of a method for coupling a data line to a modemin the communication server; and

FIG. 9 is a flow chart of a method to decouple a data line from a modemin the communication server;

FIG. 10A illustrates another implementation of the communication server;

FIG. 10B illustrates in more detail a line interface device of thecommunication server of FIG. 10A;

FIG. 10C illustrates in more detail the controller of the communicationserver of FIG. 10A;

FIG. 10D illustrates in more detail a detector of the communicationserver of FIG. 10A;

FIG. 10E illustrates in more detail a modem in the modem pool of thecommunication server of FIG. 10A;

FIG. 11A illustrates in more detail an analog filter implementation of adetector of the communication server;

FIG. 11B illustrates in more detail a tone decoder implementation of adetector of the communication server;

FIG. 11C illustrates in more detail a digital signal processorimplementation of a detector of the communication server;

FIG. 12 illustrates in more detail a digital switching matriximplementation of the switch of the communication server;

FIG. 13A illustrates in more detail a frequency multiplexingimplementation of the switch of the communications server;

FIG. 13B is a diagram of frequencies used in the switch of FIG. 13A;

FIG. 14A illustrates line interface modules and the modem pool of adistributed switching implementation of the communication server; and

FIG. 14B illustrates in more detail the line interface modules and themodem pool of the communication server of FIG. 14A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a communication system 10 that provides bothtelephone and data service to a subscriber 12. A central office 14 iscoupled to subscriber 12 using subscriber line 16. In operation, centraloffice 14 provides telephone and data service to subscriber 12 usingsubscriber line 16. Subscriber line 16 supports simultaneous telephoneand data service using twisted pair wiring.

Subscriber 12 includes a telephone 20 and a computer 22, both coupled toan interface 24. A splitter 25 is coupled to subscriber line 16 andoperates to split subscriber line 16 into a twisted pair phone line 26and a twisted pair data line 28. Phone line 26 is coupled to telephone20 using interface 24. Similarly, data line 28 is coupled to computer 22using interface 24. Subscriber 12 refers to one or more components atthe subscriber premises shown in FIG. 1, as well as the user of thesecomponents.

Telephone 20 is a traditional telephone transceiver, a cordlesstelephone transceiver, or any other device suitable for allowingcommunication over telephone line 26. Computer 22 comprises a mainframedevice, mini-frame device, server, desktop personal computer, notebookpersonal computer, or other suitable computing device having an XDSLmodem 30 that communicates data using data line 28. Modem 30 couples toother components of computer 22 using a Peripheral ComponentInterconnect (PCI) bus, an Industrial Standard Architecture (ISA) bus, aPersonal Computer Memory Card International Association (PCMCIA)interface, or any other suitable technology that provides input/outputcapability to computer 22. The selection and design of modem 30 forcomputer 22 may depend on the type or functionality of computer 22, aswell as the data service rate supported by data line 28.

Modem 30 transmits and receives data in communication system 10 usingany suitable digital subscriber line technology, referred to generallyas XDSL. Modem 30 also supports Ethernet, Fast Ethernet, V.35 dataprotocol, frame relay, asynchronous transfer mode (ATM), switchedmulti-megabit data service (SMDS), high-level data link control (HDLC),serial line Internet protocol (SLIP), point-to-point protocol (PPP),transmission control protocol/Internet protocol (TCP/IP), or any otherappropriate protocol, collectively referred to as digital protocol. Forexample, computer 22 may include a network interface 31 to receive datafrom central office 14 or to further communicate data to a local areanetwork (LAN), wide area network (WAN), or other suitable networkcoupled to computer 22 using link 18. In general, modem 30 translatesinformation between the communication protocol supported bycommunication system 10 and the digital protocol supported by computer22.

Communication system 10 includes numerous other twisted pair subscriberlines 16 coupled to other subscribers 12. In an exemplary embodiment,central office 14 provides phone and data service to one thousandsubscribers, with each subscriber 12 including one or more componentsdescribed above at its premises. The subscribers and subscriber lines incommunication system 10 are referred to collectively in the plural assubscribers 12 and subscriber lines 16.

Interface 24 couples phone line 26 to telephone 20, and data line 28 tocomputer 22. In one embodiment, interface 24 provides additionalcouplings to additional telephones 20 and computers 22 at subscriber 12.Splitter 25 is a passive or active splitter that divides subscriber line16 into phone line 26 and data line 28 of the same type. Throughout thisdescription, phone line 26 and data line 28 may be referred tospecifically, or collectively as part of subscriber line 16.

Subscriber line 16 couples subscriber 12 to central office 14.Subscriber line 16 comprises twisted pair wiring that is commonlyinstalled at subscriber premises and as the local loop in many publicswitched telephone networks (PSTNs). Subscriber line 16 may beunshielded twisted pair (UTP), shielded twisted pair (STP), or othersuitable type or category of twisted pair wiring made of copper or othersuitable material. Phone line 26 and data line 28 associated withsubscriber line 16 may be the same or different type or category oftwisted pair wiring.

Central office 14 includes a splitter 50 coupled to subscriber line 16.Like splitter 25 at subscriber 12, splitter 50 at central office 14 is apassive or active splitter that divides subscriber line 16 into atwisted pair phone line 52 and a twisted pair data line 54. Phone line52 and data line 54 associated with subscriber line 16 may be the sameor different type or category of twisted pair wiring. A telephone switch56 at central office 14 is coupled to phone line 52 to provide plain oldtelephone system (POTS) service to subscriber 12. Telephone switch 56also represents other components in the PSTN or other suitable voicecommunication network, such as switches, wireline or wireless links,satellites, microwave uplinks, and other communication facilities todeliver telephone service to subscriber 12.

A communication server 58 is coupled to splitter 50 using data line 54.As described in detail below, communication server 58 manages theprovisioning of data service to subscriber 12. Communication server 58performs off-hook detection to determine if subscriber 12 desires dataservice. Specifically, communication server 58 couples a modem tosubscriber line 16 upon detecting a need for data service from computer22. Communication server 58 tracks subscriber usage, monitors subscriberinformation, and generates billing and demographic information, asdescribed below.

The data off-hook detector in communication server 58 can use one ofseveral methods to determine whether subscriber 12 should be connectedto an XDSL modem. The off-hook detector may monitor direct currentvoltages, electrical tones, data link frames, or any other protocol ordata sequencing to determine whether subscriber 12 needs data access.The off-hook detector in communication server 58 may monitor electricaltones generated by modem 30 while in the process of training, notching,equalizing, or performing any other task that puts electrical tones ontosubscriber line 16 and its associated data line 54. Communication server58 may also detect frames or packets. These frames or packets could beEthernet, ATM, HDLC, or any suitable data communications frame format.The off-hook detector in communication server 58 could also examinevarious protocols such as TCP/IP, PPP, or any other suitable networkprotocol or data stream.

Communications server 58 multiplexes modem digital outputs into amultiplexed digital line 62 for delivery to a router or other networkdevice 60. In one embodiment, multiplexed digital line 62 carries asingle bidirectional and multiplexed signal for all subscribers 12 incommunication system 10. Signals on multiplexed digital line 62 maysupport any appropriate digital protocol used by network device 60. Acommunication network 64, such as a global communication network likethe Internet, is coupled to network device 60. Communication network 64may also include a synchronous optical network (SONET), a frame relaynetwork, an asynchronous transfer mode (ATM) network, a T1, T3, E1, orE3 network, or any other suitable communication network.

One important technical advantage of the present invention is theability to over-subscribe the XDSL communication facilities ofcommunication server 58 to service an increasing number of subscribers12 in communication system 10. Communication server 58 may couple to thesame number and type of data lines 54 as represented by subscriber lines16 in communication system 10. For example, if central office 14services one thousand subscribers 12 using twisted pair subscriber lines16, then data lines 54 coupled to communication server 58 may representas many as one thousand twisted pair lines.

In one embodiment, not all subscribers 12 in communication system 10desire access to data service provided by communication server 58.Splitter 50 need not provide a separate data line 54 for thosesubscribers 12 that only desire phone service from telephone switch 56.As more subscribers 12 desire access to data service, the XDSLcommunication capabilities of splitter 50 and communication server 58may be supplemented in a modular and cost effective manner to meet thedemand.

Communication system 10 supports data service over subscriber lines 16using asymmetric digital subscriber line (ADSL), symmetric digitalsubscriber line (SDSL), high-speed digital subscriber line (HDSL), veryhigh-speed digital subscriber line (VDSL), or any other suitabletechnology that allows high rate data service over twisted pair wiring.All of these technologies are referred to collectively as XDSL orcommunication protocol. In one embodiment, subscriber line 16 andcomponents of subscriber 12 and central office 14 support communicationusing ADSL techniques that comply with ANSI standard T1.413. In anotherembodiment, ADSL communication over subscriber line 16 may be performedusing the carrier-less amplitude phase modulation (CAP) techniquedeveloped by AT&T Corporation.

In an ADSL communication system, the downlink data rate 32 from centraloffice 14 to subscriber 12 is greater than the uplink data rate 34 fromsubscriber 12 to central office 14. This allows high bandwidthcommunication to subscriber 12, while still providing lower bandwidthcommunication to central office 14. ADSL communication is well-adaptedfor applications, such as video-on-demand, multimedia, and Internetaccess, that transfer large volumes of information to subscriber 12 inresponse to shorter requests for information. In one specificembodiment, downlink data rate 32 is approximately 1.5 Mbps, whereasuplink data rate 34 is approximately 750 kbps. In other embodiments,downlink data rate 32 may be six Mbps or more depending on the specificXDSL technology employed, the quality and length of subscriber line 16,and the contribution of noise and distortion from other components incommunication system 10.

XDSL technology provides data service using existing subscriber lines 16without interrupting normal telephone service. This is accomplished by aseparation technique, such as frequency division multiplexing (FDM), toseparate frequencies that provide telephone service from thosefrequencies that provide data service. Dynamic noise cancellationtechniques and a guard band between the data and phone servicefrequencies ensure reliable and simultaneous access to data and phoneservice over subscriber line 16. For example, subscriber 12 maysimultaneously engage in both a data communication session usingcomputer 22 and a voice conversation using telephone 20.

In operation, communication system 10 provides phone and data service tosubscriber 12. Subscriber 12 accesses phone service by using telephone20 to initiate a call. Upon going off-hook, communication system 10establishes a circuit between telephone 20 and telephone switch 56 usinginterface 24, phone line 26, splitter 25, subscriber line 16, splitter50, and one of phone lines 52. Upon establishing this telephone circuit,subscriber 12 using telephone 20 receives POTS service from telephoneswitch 56.

To access data service, subscriber 12 turns on computer 22, executes aprogram, such as an Internet browser, or performs some other affirmativeor passive activity that generates a request, command, data packet,electrical tone, or other suitable information or signal that indicatesa need for data service. In one embodiment, modem 30 repetitivelytransmits the need for data service in a request interval, where therequest interval comprises the time length of the request and the silentinterval until the next request. Alternatively, the need for dataservice indicated at subscriber 12 may be based on the establishment ofa closed circuit between subscriber 12 and central office 14 or on oneor more analog or digital signal transitions. Modem 30 communicates theneed to communication server 58 at central office 14 using interface 24,data line 28, splitter 25, subscriber line 16, splitter 50, and one ofdata lines 54.

As described in detail below, communication server 58 detects the needfor data service and selects an XDSL modem at communication server 58 tocommunicate with XDSL modem 30 in computer 22. Upon establishing a modemconnection between modem 30 in computer 22 and a selected modem incommunication server 58, subscriber 12 engages in a data communicationsession with communication network 64 using network device 60. Inaddition, computer 22 may function as a gateway into communicationnetwork 10 for other devices coupled to network interface 31 using link18.

XDSL technology allows simultaneous use of subscriber line 16 for bothphone and data service using the existing twisted pair wiring incommunication system 10. In one embodiment, splitter 50, communicationserver 58, and network device 60 are located at central office 14 toprovide an efficient and modular provisioning of XDSL data service tosubscribers 12. However, splitter 50, communication server 58, andnetwork device 60 may be located outside central office 14 withoutdeparting from the scope of the present invention.

FIG. 2 illustrates in more detail communication server 58. Data lines 54associated with subscriber lines 16 are coupled to a switch 70. In oneembodiment, each data line 54 corresponds to an associated subscriberline 16 and its related subscriber 12. Switch 70 couples selected datalines 54 to output lines 72 that in turn couple to modem pool 74. Theformat of signals on data lines 54 and output lines 72 is the same asthe format of signals on subscriber lines 16. For example, ifcommunication system 10 adopts XDSL technology, signals on data lines 54and output lines 72 are modulated using XDSL techniques.

Modems in modem pool 74 convert signals in an appropriate XDSLcommunication protocol into digital data in an appropriate digitalprotocol on digital lines 76. A multiplexer 78 is coupled to digitallines 76 and combines the signals on digital lines 76 into a fewernumber of multiplexed digital lines 62. In one embodiment, multiplexer78 combines information for delivery to network device 60 using a singlemultiplexed digital line 62.

A controller 80 is coupled to data lines 54 using a link 82. Controller80 is also coupled to switch 70 and modem pool 74 using links 84 and 86,respectively. Controller 80 detects a need for data service generated bysubscribers 12 and communicated over subscriber lines 16 to data lines54. In response, controller 80 using link 84 directs switch 70 to couplea selected subset of data lines 54 to selected output lines 72 thatcouple to modems in modem pool 74. For example, controller 80 maymonitor one thousand data lines 54 to provide XDSL data services usingone hundred modems in modem pool 74.

Controller 80 also receives information from modem pool 74 using link 86to determine status information of modems in modem pool 74. As digitallines 76 become inactive for a predetermined period of time, modem pool74 detects this inactivity and generates a timeout indication forcommunication to controller 80. Upon receiving the timeout indication,controller 80 releases the inactive modem in modem pool 74 for lateruse.

In operation, communication server 58 detects a need for data service ona selected data line 54. This need may be indicated by current voltages,electrical tones, data link frames, packets, or any other suitableanalog or digital protocol or data sequencing. Controller 80 detects theneed using link 82 and configures switch 70 to provide a couplingbetween the selected data line 54 and one of the output lines 72 coupledto a selected modem pool 74. The selected modem translates bidirectionalcommunication between a communication protocol on output line 72 and adigital protocol on digital line 76. Multiplexer 78 translatesinformation between digital lines 76 and one or more multiplexed digitallines 62.

FIG. 3 illustrates in more detail controller 80. Data lines 54 throughlink 82 are coupled to polling circuitry 100. In one embodiment, pollingcircuitry 100 includes a number of terminals 102 corresponding to eachdata line 54. A switch 104 having a conductive probe 106 contactsterminals 102 to sample the signal on the associated data line 54.Polling circuitry 100 may comprise electromagnetic components, such as arelay or switch, solid state circuitry, or both. It should be understoodthat the present invention embodies any polling circuitry 100 thatallows successive or selective sampling of data lines 54.

Transceiver 108 receives a selected signal 110 from polling circuitry100. A detector 112 is coupled to transceiver 108, which in turn iscoupled to processor 116. Detector 112 may include a media accesscontroller (MAC) and associated memory to detect and store frames orpackets of an appropriate digital protocol. Detector 112 may alsoinclude less complicated circuitry to detect current voltages,electrical tones, data bit transmissions, or other analog or digitalinformation generated by transceiver 108.

Transceiver 108 and detector 112 may collectively be represented asmodem 115, as indicated by the dashed line. Modem 115 provides aninterface between the XDSL communication protocol of communicationsystem 10 and processor 116. Modem 115 also includes similar componentsand performs similar functions as modem 30 in computer 22 to enablemodem 30 and modem 115 to exchange information using XDSL technology.Throughout this discussion, the term detector may refer to detector 112or collectively modem 115.

A processor 116 is coupled to detector 112 and controls the overalloperation of controller 80. A timer 117 is coupled to processor 116.Processor 116 is coupled to input/output circuitry 118, which in turn iscoupled to switch 70 and modem pool 74 using links 84 and 86,respectively. Processor 116 is also coupled to switch 104 of pollingcircuitry 100 using input/output circuitry 118. In one embodiment,processor 116 controls the data line selection, dwell time, and othersuitable parameters of polling circuitry 100.

Processor 116 is also coupled to database 120 that includes a program121, an activity table 122, a line profile table 124, and a subscribertable 126. Database 120 stores information as one or more tables, files,or other data structure in volatile or non-volatile memory. All or aportion of database 120 may reside at controller 80, withincommunication server 58, within central office 14, or at anotherlocation in communication system 10. For example, several communicationservers 58 in one or more central offices 14 can access database 120stored in a central location to provide more intelligent management andprovisioning of XDSL data service in communication system 10. One ormore central offices 14 may be coupled together and the resources oftheir associated communication servers 58 shared using simple networkmanagement protocol (SNMP) techniques.

Program 121 contains instructions to be executed by processor 116 toperform the functions of controller 80. Program 121 may reside indatabase 120 as shown or may be integral to memory components intransceiver 108, detector 112, and/or processor 116. Program 121 may bewritten in machine code, pseudocode, or other appropriate programminglanguage. Program 121 may include modifiable source code and otherversion control features that allow modification, debugging, andenhancement of the functionality of program 121.

Activity table 122, described in more detail below with reference toFIG. 7, maintains status information on data lines 54, switch 70, andoutput lines 72. In particular, activity table 122 contains informationon inactive and active data lines 54, data lines 54 corresponding tocurrent valid subscribers 16 of XDSL data service, and the mappingperformed by switch 70 between data lines 54 and output lines 72.Moreover, activity table 122 includes information that specifies theinactivity of a modem in modem pool 74, the status of a data line 54 asdedicated, and any other suitable information that enables processor 116to monitor and control the operation of switch 70 and modem pool 74.

Profile table 124 stores profile information on data lines 54. Thisprofile information reflects electrical or physical characteristics ofdata line 54, its associated subscriber line 16 and data line 28,intervening components such as interface 24, splitter 25, splitter 50,and polling circuitry 100, as well as any other component or factor thateffects the performance or electrical characteristics of signalsreceived on data lines 54. Processor 116 may access profile table 124and provide profile information to transceiver 108 using link 125.Alternatively, transceiver 108 may be a more robust and broadband devicethat does not need profile information from profile table 124. Processor116 may also provide profile information to program XDSL modems in modempool 74 once a coupling is made to a selected data line 54. Theexistence and complexity of profile information in profile table 124depends on the requirements of transceiver 108 and XDSL modems in modempool 74, as well as the complexity of signals that indicate a need fordata service from subscriber 12.

Subscriber table 126 stores subscriber information indexed by one ormore identifiers of subscriber 12, computer 22, modem 30, subscriberline 16, or other information that associates data line 54 with aparticular subscriber 12. Subscriber table 126 includes subscriberconnect times, session duration, session activity, session logs, billingdata, subscriber account information, and any other suitable subscriberinformation. This information may be summarized and additionalinformation included to generate billing and demographic data onsubscribers 12 in communication system 10.

For example, subscriber table 126 may maintain summary statistics on thenumber of subscribers 12 served by communication server 58, the averageconnect time, load factors, time-of-day connection profiles, and otherstatistics to assess the communication facilities to be deployed atcommunication server 58, the over-subscription ratio that can besupported by communication system 10, and other provisioning andmanagement issues. Furthermore, subscriber table 126 may combinesubscriber information from one or more communication servers 58 in oneor more central offices 14 in communication system 10.

Management interface 128 is coupled to processor 116 and database 120and allows external access to the functionality of processor 116.Management interface 128 is also coupled to database 120, which allowsmodification of program 121, as well as remote access and modificationof information in activity table 122, profile table 124, and subscribertable 126. In one embodiment, the telephone service provider or otherentity that operates central office 14 or communication system 10accesses management interface 128 to provide management and control overthe operations of controller 80 and communication server 58. Forexample, the telephone service provider uses management interface 128 toaccess activity table 122 and/or subscriber table 126 to update thevalid subscribers 12 that have access to communication server 58. Alocal or remote computer 130 is coupled to program interface 128 usingan appropriate data link 132, such as a serial RS-232 link, to providethis management feature.

In operation, modem 30 in computer 22 indicates a need for data service,and communicates this need to an associated data line 54 using interface24, data line 28, splitter 25, subscriber line 16, and splitter 50. Inone embodiment, modem 30 transmits successive requests at apredetermined request interval. Processor 116 accesses activity table122 to determine which data lines 54 to poll, depending on the active orinactive status of the data line 54, whether subscriber 12 correspondingto data line 54 is a current and valid subscriber, and other appropriateconsiderations. For example, activity table 122 may indicate valid andnon-dedicated subscribers 12 to poll.

Polling circuitry 100 successively polls selected data lines 54, asdirected by processor 116, using link 82 to detect a need for dataservice. For each data line 54 polled, processor 116 may access profiletable 124 in database 120 and provide associated profile information totransceiver 108 using link 125. Polling circuitry 100 dwells on eachdata line 54 for a predetermined polling interval to detect a need. Inone embodiment, the polling interval is at least two times a requestinterval of modem 30.

Upon detecting the need for data service associated with a selected dataline 54 from polling circuitry 100, transceiver 108 may translate theinformation from the selected XDSL communication protocol employed onsubscriber line 16 into digital or analog data for detection by detector112. A media access controller (MAC) in detector 112 may transformserial digital data from transceiver 108 into a parallel digital format.Detector 112 receives the information translated by transceiver 108, andstores this information in a suitable memory location for access byprocessor 116. Processor 116 periodically accesses detector 112 todetermine if a need for data service has been detected.

Upon detecting a need for data service, processor 116 accesses database120 to determine the availability and status of modems in modem pool 74.Processor 116 selects an available modem from modem pool 74. Processor116 then directs switch 70 to make the appropriate coupling betweenselected data line 54 and output line 72 coupled to the selected modem.Upon establishing coupling between modem 30 in computer 22 at subscriber12 and a selected modem in modem pool 74, controller 80 continues tomonitor the remaining data lines 54 using polling circuitry 100.

Processor 116 can transmit status or connection information to modem 30in computer 22 using transceiver 108. This may be performed before,during, or after coupling the selected modem in modem pool 74 to dataline 54. For example, processor 116 may send acknowledgment informationto modem 30 that includes an indication that a modem is or is notavailable, an identification of the available modem, a time intervalbefore modem 30 should attempt communication with the selected modem inmodem pool 74, or any other suitable information. Furthermore, processor116 may access information from subscriber table 126, such as billingand account information, historical connection information, or othersuitable subscriber information, and transmit this information separateto or as part of the acknowledgment information described above.

Processor 116 may also transmit connection information and updatedbilling and subscriber information to modem 30 at computer 22 using link86 and the associated XDSL modem in modem pool 74. This information mayinclude the length of the current session, the current balance in theaccount of subscriber 12, as well as any other suitable information thatrelates to the account or activity of subscriber 12 with communicationserver 54. Generally, processor 116 may communicate any suitableinformation stored at or made available to controller 80 to subscribers12 using transceiver 108 or the associated modem in modem pool 74.

FIG. 4 illustrates in more detail switch 70 and modem pool 74 ofcommunication server 58. Data lines 54 are coupled to switch 70, nowshown in more detail as a cross-bar or cross-point matrix switch. Inthis particular embodiment, data lines 54 correspond to lines 150, andoutput lines 72 correspond to lines 152 in switch 70. The number oflines 150 (n) is greater than the number of lines 152 (m). This allowsswitch 70 to couple selected data lines 54 to a reduced number of outputlines 72 to provide an over-subscription of XDSL data service incommunication system 10. For example, switch 70 couples the second oflines 150 to the last of lines 152 by establishing connection 154.Similarly, switch 70 couples the last of lines 150 and the first oflines 152 by establishing connection 156.

Although switch 70 is shown in FIG. 4 to be a cross-bar or cross-pointmatrix switch, it should be understood that any device that can couple anumber of data lines 54 to a reduced number of output lines 72 may beused. Switch 70 may incorporate electromagnetic components, such asrelays and contacts, or may be implemented in whole or in part using oneor more solid state devices.

Modem pool 74 includes XDSL modems 160 associated with output lines 72from switch 70. Modems 160 translate information between an appropriateXDSL communication protocol on output lines 72 and an appropriatedigital protocol on digital lines 76. In one embodiment, modems 160 maybe similar in construction and operation to modem 30 at subscriber 12. Adetector 162 coupled to modems 160 detects the activity of modems 160 todetermine if the line has become inactive for a predetermined intervalof time. For example, if one of the modems 160 does not display activityover a five-minute interval, detector 162 generates a timeout indicationto notify processor 116 of the inactive modem. Processor 116 releases ordecouples the inactive modem for later subscriber sessions. In oneembodiment, detectors 162 may include one-shot timers or otherretriggerable timers set for a predetermined time interval to detect theinactive status of modems 160.

Detector 162 is a monitoring circuit that passes through the digitaloutput of modems 160 to digital lines 76 for presentation to multiplexer78. Multiplexer 78 may combine signals from digital lines 76 into asingle multiplexed digital line 62. Alternatively, multiplexer 78 mayemploy any suitable reduction ratio that places signals on digital lines76 on a fewer number of multiplexed digital lines 62.

Processor 116 may directly communicate with modems 160 using link 164.For example, link 164 allows processor 116 to program modems 160 withprofile information retrieved from profile table 124. Link 164 alsosupports communication between processor 116 and selected subscribers 12during an active subscriber session using modems 160. Moreover, link 164allows processor 116 to monitor the information received from andtransmitted to subscribers 12 during a communication session.

In operation, switch 70 couples a selected subset of data lines 54 tooutput lines 72 in response to signals received from controller 80 usinglink 84. Each of the output lines 72 is coupled to an associated modem160 which translates the information formatted in an analogcommunication protocol, such as XDSL, into an appropriate digitalsignal. The digital information output from modems 160 passes throughdetector 162, which monitors the activity on the output line of modems160. If detector 162 senses inactivity over a predetermined interval, atimeout indication is provided to processor 116 using link 86. Signalson digital lines 76 may be reduced to fewer multiplexed digital lines 62using multiplexer 78.

FIG. 5 illustrates in more detail transceiver 108 in controller 80. Toreceive information, transceiver 108 includes filters and magnetics 170to condition the signal from selected data line 54. The conditionedsignal is provided over differential lines 172 to analog bit pump 174.Bit pump 174 performs the specific demodulation technique for the chosenXDSL communication protocol. For example, bit pump 174 may execute adiscrete multi-tone demodulation (DMT) or carrierless amplitude phasedemodulation (CAP) to demodulate an XDSL signal on differential lines172 into a digital stream on line 176. Logic and timing circuitry 178contains decode logic, timing and synchronization circuitry, steeringlogic, and other appropriate digital processing circuitry to produce adata signal on receive data line 180 and a corresponding clock signal onclock line 182 for delivery to detector 112 or processor 116. Detector112 may include a MAC to support any digital protocol or signaldetection that indicates a need for XDSL data service. The data may bein non-return-to-zero format or any other suitable format.

To transmit information, transceiver 108 receives a data signal ontransmit data line 184 from detector 112 or processor 116. Using theclock line 182, logic and timing circuitry 178 digitally processessignals received on transmit data line 184 for delivery to analog bitpump 174. Using an appropriate modulation technique, such as DMT or CAP,analog bit pump 174 produces an analog signal for delivery overdifferential lines 172 to filters and magnetics 170 for transmissionover selected data line 54.

FIG. 6 illustrates in more detail a specific embodiment of detector 112that includes a MAC 113 and a memory 114. MAC 113 is coupled to receivedata line 180 and clock line 182, and translates received data from aserial data format, such as a non-return-to-zero format, into anappropriate parallel digital format. MAC 113 translates the data fromthe chosen digital protocol and provides the data to memory 114 usingdata bus 190. MAC 113 also provides an address to memory 114 usingaddress bus 192 to specify the location in memory 114 to store dataprovided on data bus 190. In addition, MAC 113 provides a write signalto memory 114 using control line 194.

To transmit data, MAC 113 provides a read signal to memory 114 usingcontrol line 194, and an associated address of the data to be read usingaddress bus 192. In response, memory 114 provides the requested data ondata bus 190. MAC 113 translates the data into the selected digitalprotocol for placement on transmit data line 184.

FIG. 7 illustrates one embodiment of activity table 122 stored indatabase 120 of controller 80. Processor 116 accesses and modifiesentries in activity table 122 to direct the operation of controller 80.In addition, management interface 128 provides external access toactivity table 122. For example, a telephone service provider usingmanagement interface 128 can add, delete, or otherwise modify entries inactivity table 122 to maintain a listing of valid subscribers 12.Database 120 stores some or all of the status information shown in thisexemplary activity table 122, as well as other information that may beused by processor 116 to direct the activities of controller 80.

Activity table 122 includes a data line column 200 that contains anaddress or other appropriate identifier of data lines 54 associated withsubscriber lines 16 and their related subscribers 12. Status column 202indicates the status of data line 54 identified in data line column 200.For example, status column 202 may contain one or more indications thatthe associated data line 54 is inactive (I), active (A), or dedicated(D). A timeout column 204 indicates whether detector 162 in modem pool74 has detected a timeout associated with a particular data line 54. Amodem column 206 includes an identifier of the modem 160 associated withthe corresponding data line 54.

An entry in activity table 122 corresponds to a row that designates aselected data line 54 in data line column 200, the status of theselected data line 54 in status column 202, a timeout indication of theselected data line 54 in timeout column 204, and the modem associatedwith the selected data line 54 in modem column 206. For example, entry208 relates to data line “D1” which is inactive. Entry 210 representsdata line “D2” which is inactive but dedicated to modem “M1.” Entry 212indicates that data line “D4” is active, coupled to modem “M3,” but atimeout indication has been detected.

Subscribers 12 indicated in status column 202 as dedicated may beserviced by communication server 58 in a specific way. Switch 70 incommunication server 58 maintains a coupling between data line 54corresponding to dedicated subscriber 12 and its associated anddedicated modem 160. In this manner, controller 80 need not detect aneed for data service or reconfigure the couplings for data line 54corresponding to dedicated subscriber 12. In this manner, communicationserver 58 provides the option of a different class of service for adedicated subscriber 12 that desires uninterrupted access to XDSLcommunication facilities.

FIG. 8 is a flow chart of a method performed at controller 80 to coupledata lines 54 to modems 160 in modem pool 74. The method begins at step300 where processor 116 of controller 80 loads activity table 122 fromdatabase 120 which contains an entry for each valid subscriber 12 servedby communication server 58. Using management interface 128, a telephoneservice provider may ensure that activity table 122 reflects validsubscribers 12 by monitoring past due accounts, the overuse of dataservice, successive invalid attempts to access communication server 54,or other factors that may cause subscribers 12 to be invalid. Processor116 selects the first inactive and non-dedicated data line 54 indicatedby the designation “I” in status column 202 of activity table 122. Sinceswitch 70 is configured to continuously couple dedicated subscribers 12to their dedicated modems 160, processor 116 need not select an inactivedata line 54 that is also dedicated, as indicated by the designation“I/D” in status column 202.

Using input/output circuitry 118, processor 116 directs switch 104 ofpolling circuitry 100 to couple transceiver 108 to the selected inactiveand non-dedicated data line 54 at step 304. If appropriate, processor116 accesses profile table 124 in database 120 and provides profileinformation for the selected data line 54 to transceiver 108 using link125 at step 306. Processor 116 initializes timer 117 with apredetermined polling interval at step 308.

If a need for data service has not been detected by transceiver 108 atstep 312, then processor 116 checks timer 117 at step 314. If thepolling interval monitored by timer 117 has not expired at step 314,then processor 116 again determines if a need has been detected at step312. However, if the polling interval monitored by timer 117 has expiredat step 314, processor 116 selects the next inactive and non-dedicateddata line 54 as indicated in status column 202 of activity table 122 atstep 316, and returns to step 304.

If a need for data service is detected at step 312, the associatedinformation may be further processed by detector 112 and placed inmemory for access by processor 116 at step 318. Before, during, or afterstep 318, transceiver 108, detector 112, and/or processor 116 mayvalidate the need for data service. Validation may be performed at a lowlevel, such as a verification of the checksum or detection of anincomplete transmission, or at a higher level, such as a verification ofan identifier, password, or other security information that providesaccess to communication server 58. Validation contemplates any level ofvalidation or security handshake that confirms that the received need isvalid and accepted by controller 80.

Upon selecting an unused modem at step 332, processor 116 generates acommand that directs switch 70 to couple the selected data line 54 tothe selected modem 160 at step 333. Processor 116 may communicate statusor connection information to subscriber 12 using transceiver 108 or theselected modem 160 at step 334. Processor 116 updates activity table 122at step 336 to indicate that the selected data line 54 is now active andthat the selected modem 160 is now being used. Processor 116 directsactivity detector 162 to initialize the inactivity interval for theselected modem 160 at step 338. Processor 116 then selects the nextinactive and non-dedicated data line 54 in activity table 122 at step316, and returns to step 304.

FIG. 9 is a flow chart of a method for monitoring and decoupling modems160 due to inactivity. It should be understood that the methodsdescribed with reference to FIGS. 8 and 9 may be performedsimultaneously or in alternative succession by processor 116 to coupleand decouple data lines 54 with modems 160. The method begins at step400 where processor 116 loads activity table 122 which contains an entryfor each valid subscriber 12 served by communication server 58.Processor 116 selects a first active and non-dedicated data line 54 asindicated by the designation “A” in status column 202 of activity table122 at step 402. Since switch 70 is configured to maintain a couplingbetween dedicated subscribers 12 and their dedicated modems 160,processor 116 need not select an active data line 54 that is alsodedicated, as indicated by the designation “A/D” in status column 202.

Processor 116 retrieves timeout status for modem 160 associated with theselected active data line 54 from detector 162 using link 86 andinput/output circuitry 118 at step 404. Processor 116 determines if atimeout has occurred for the selected active data line 54 at step 408.If a timeout has not occurred, processor 116 selects the next active andnon-dedicated data line 54 as indicated in status column 202 of activitytable 122 at step 410, and returns to step 404.

If a timeout has occurred at step 408, processor 116 may communicatestatus or connection information to subscriber 12 associated with theselected active data line 54 using transceiver 108 or the associatedmodem 160 at step 412. Processor 116 generates a command to directswitch 70 to decouple the active data line 54 from its associated modem160 at step 414. Processor 116 updates activity table 122 at step 416 toindicate that data line 54 is now inactive and that the associated modem160 is available for another subscriber session.

FIG. 10A illustrates another implementation of communication server 58in communication system 10. Communication server 58 of FIG. 10A isdifferent from the implementation described above in that it providesswitching at an isolated four-wire interface although much of thecomponents and functions otherwise are the same. As shown in FIG. 10A,data lines 54 are coupled to and received by a plurality of lineinterface units 500. Each line interface 500 provides an analoginterface, line driver and transformer for processing signals on datalines 54. Each line interface unit 500 is coupled to a switching matrix502 and communicates with switching matrix 502 across a transmit datapair 504 and a receive data pair 506. Each line interface unit 500operates to interface between transmit data pair 504 and receive datapair 505 and twisted pair data line 54.

In the implementation of FIG. 10A, a detector 508 is coupled to eachreceive data pair 506. Each detector 508 operates to detect a requestfor service on the associated receive data pair 506 and, upon detection,provides a signal to controller 80 indicating a request for service.Detector 508 is shown in more detail in FIG. 10D, and implementations ofdetectors are shown in more detail in FIGS. 11A, 11B and 11C. It shouldbe understood that other implementations can combine polling withmultiple detectors to reduce the number of inputs to controller 80 andto reduce the number of detectors. For example, FIG. 3 shows animplementation using polling circuitry 100 that can be used with thedetector in the communications server embodiment of FIG. 10A.

As shown, switching matrix 502 is coupled to a modem pool 510 andcommunicates with modem pool 510 across transmit data pairs 512 andreceive data pairs 514. Transmit data pairs 512 and receive data pairs514 contain a number of pairs equal to the number of modems in modempool 510. As described above, modems in modem pool 510 convert signalsin an appropriate XDSL communication protocol into digital data in anappropriate digital protocol on digital lines 76. Multiplexer 78 is thencoupled to digital line 76 and provides a multiplexed digital lineoutput 62. Also as described above, controller 80 provides switchcontrol signals 84 to switching matrix 502 and communicates modemselection and control information 86 with modem pool 510.

In operation, each detector 508 detects a request for service on theassociated receive data pair 506 and informs controller 80 that arequest for service has occurred. Controller 80 then checks which modemsin model pool 510 are assigned and which data lines 54 are valid.Controller 80 assigns a modem from modem pool 510 to the requesting dataline 54 using switching matrix 502 to connect the associated receivedata pair 506 and transmit data pair 504 to the appropriate receive datapair 514 and transmit data pair 512.

A technical advantage of providing switching at a four-wire interfacewithin communication server 58 is that switching matrix 502 is isolatedfrom data lines 54 and subscriber lines 16 by transformers in lineinterface units 500. Because of this isolation, switching matrix 502 canoperate without constraints imposed by technical requirements forinteraction with data lines 54 and subscriber lines 16. For example, theisolation of switching matrix 502 allows CMOS switches to be used ratherthan more expensive solid state relays or mechanical relays.

FIG. 10B illustrates in more detail line interface device 500 ofcommunication server 58 of FIG. 10A. Line interface device 500 includesa line protection circuit 520 that is coupled to and receives data line54. Line protection circuit 54 operates to ensure that activity downstream in communication server 58 does not affect the integrity of dataline 54. Line protection circuit 520 is coupled to a magnetics/hybridunit 522. Magnetics/hybrid unit 522 can comprise a transformer andoperates to interface between the data line and an internal transmitdata pair 524 and receive data pair 526. Magnetics/hybrid unit 522 alsoisolates the four-wire interface provided by internal receive data pair526 and transmit data pair 524 from data line 54.

A line receiver 528 receives receive data pair 526 and drives signals toa receive filter 530. The output of receive filter 530 is receive datapair 506 which is coupled to switching matrix 502 as shown in FIG. 10A.Similarly, transmit data pair 504 is coupled to a transmit filter 532which provides signals to a cable driver 534. Cable driver 534 thendrives signals on transmit data pair 524 to magnetics/hybrid unit 522.

FIG. 10C illustrates in more detail controller 80 of communicationserver 58 where a plurality of detectors provide indications of arequest for service. Controller 80 of FIG. 10C includes processor 116and input/output circuitry 118 as discussed above with respect to FIG.3. Controller 80 also includes a scanner or processor interrupt circuit540 which receives the request for service indications from detectors508 and provides a scanner output or processor interrupt to processor116. This allows the outputs of a number of detectors 508 to be sampledto provide an appropriate signal to processor 116 when a request forservice has been detected. As mentioned above, it should be understoodthat selection of the number of detectors and the amount of polling canbe made as appropriate for the desired application. In oneimplementation, scanner or processor interrupt circuit 540 comprises agate array having logic circuitry for generating appropriate interruptsignals to processor 116.

FIG. 10D illustrates in more detail a detector 508 of communicationserver 58. As shown, detector 508 includes a receiver circuit 550 and aservice request detector 552. Receiver circuit 550 is coupled to areceive data pair 506 and provides an output to service request detector552. Service request detector 552 then operates to identify a requestfor service. Upon detection, service request detector 552 provides asignal indicating a request for service to controller 80. For ADSLsystems (e.g., CAP and DMT), the request for service can be an initialtone that is a pure sinusoid or a modulated sinusoid. Threeimplementations of a detector 508 are illustrated in more detail inFIGS. 11A, 11B and 11C and described below.

FIG. 10E illustrates in more detail a modem 560 in modem pool 510 ofcommunication server 58. Modem 560 is analogous to modem 108 of FIG. 5with filters and magnetics 170 removed. Modem 560 includes a bit pump174 which communicates with switching matrix 502 across receive datapair 526 and transmit data pair 524. Modem 560 does not need to includefilters and magnetics 170 because of the functions provided by lineinterface units 500 to create the four-wire interface described above.Bit pump 174 and logic and timing circuitry 178 otherwise operate asdiscussed with respect to FIG. 5. Conceptually, the implementation ofFIG. 10A moves the function of filters and magnetics 170 of modem 108 toline interface units 500 to isolate switching matrix 502 from data lines54.

FIG. 11A illustrates in more detail an analog filter implementation of adetector 508 of communication server 58. Detector 508 of FIG. 11Adetects the tone or modulated tone using an analog filter circuit tunedto the distinct frequency used to transmit a subscriber request forservice. Detector 508 comprises a differential receiver 570 that iscoupled to an associated receive data pair 506. Differential receiver570 is coupled to and provides a signal to a band pass filter 572. Bandpass filter 572 is coupled to a gain device 574 which is coupled to asignal processing circuit 576. The output of signal processing circuit576 is coupled to a rectifier circuit 578 which is coupled to a low passfilter 580. The output of low pass filter 580 is then provided as oneinput to a voltage comparator 582. The other input to voltage comparator582 is connected to a reference voltage 584.

In operation, detector 508 operates to detect a tone or modulated tonethat indicates a request for service on receive data pair 506.Differential receiver 570 produces a voltage output which is filtered byband pass filter 572 and provided to gain device 574. Gain device 574then amplifies the signal and provides it to signal processing circuit576. The signal processing circuit 576 processes or demodulates the XDSLsignals generated at the customer location that indicate a request fordata service. Signal processing circuit 476 provides the signal torectifier circuit 578 that outputs the signal to low pass filter 580.Low pass filter 580 filters low frequency noise to provide a DC voltageas an input to voltage comparator 582. Voltage comparator 582 comparesthat DC voltage with reference voltage 584 and outputs a logic high whenthe DC voltage is greater than reference voltage 584. Reference voltage584 is set so that voltage comparator 582 signals a request for serviceonly when the appropriate tone or modulated tone is present on receiverdata pair 506.

It should be understood that detector 508 of FIG. 11A, as well as thoseof FIGS. 11B and 11C, can be connected to polling circuit 100 of FIG. 3or other polling circuits to reduce the number of detectors required orto scan the outputs of the detectors. The number of lines that can bepolled by a single polling circuit is generally limited by the amount oftime that is required by the detector to reliably detect the subscriberrequest for service.

FIG. 11B illustrates in more detail a tone decoder implementation ofdetector 508 of communication server 58. Detector 508 comprises adifferential receiver 590 that is coupled to receive data pair 506 andprovides an output to a band pass filter 592. Band pass filter 592 iscoupled to a gain device 594 which provides an output to a signalprocessing circuit 596. The signal processing circuit 576 processes ordemodulates the XDSL signals generated at the customer location thatindicate a request for data service. The output of signal processingdevice 596 is then coupled to a tone decoder circuit 598. Tone decoderintegrated circuit 598 provides an output to controller 80 indicating arequest for service upon detection.,

In one implementation, tone decoder circuit 598 comprises an integratedcircuit, and specifically is an LMC567 tone decoder available fromNATIONAL SEMICONDUCTOR. In this implementation, tone decoder circuit 598includes a phase locked loop detector for identifying the tone ormodulated tone that indicates a request for service. The phased lockedloop detects when the received tone or modulated tone matches thesignaling frequency, and the tone detector circuit responds by signalinga request for service.

FIG. 11C illustrates in more detail a digital signal processorimplementation of detector 508 of the communication server 58. Detector508 of FIG. 11C comprises a polling circuit 600 that is coupled to aplurality of receive data pairs 506. Polling circuit selects eachreceive data pair 506 and connects it to a line receiver 602. Linereceiver 602 is coupled to a filter 604 which is coupled to ananalog/digital converter 606. Analog/digital converter converts thesignal to a digital signal and provides an output to a digital signalprocessor 608. Upon detection, digital signal processor provides arequest for service indication to controller 80.

In the implementation of FIG. 11C, polling circuitry 600 connects linereceiver 602, filter 604, analog/digital converter 606 and digitalsignal processor 608 to each line in succession. Digital signalprocessor 608 reads the data from the analog/digital converter 606 anddemodulates or detects the request for service. The dwell time forpolling circuitry 600 can be set, for example, such that detector 508can poll the lines in less than half the duration of the subscriberrequest for service tone or modulated tone. The number of lines that canbe polled by a single digital signal processor 608 is then determined bythe amount of time required for digital signal processor 608 to reliablyperform the detection algorithm and the duration of the tone describedabove.

Digital signal processor 608 is programmable to detect the subscriberrequest for service tone or modulated tone using an appropriate tonedetection algorithm or demodulation algorithm. One advantage provided bythe detector implementation of FIG. 11C is this programmability of thealgorithm within digital signal processor 608.

It should be understood that the tones used to indicate service in theabove description of FIGS. 11A, 11B, and 11C, may be the tone used instandard non-switched applications of XDSL modems, or may be additionaltones added specifically to facilitate detection in switching.

FIG. 12 illustrates in more detail a digital switching matriximplementation of communication server 58. The implementation of FIG. 12is appropriate for both a two-wire and four-wire interface to providedigital switching of the modem connections. Communications server 58 ofFIG. 12 includes line interface components and data off-hook detectionunits 610 that interface with subscriber lines 54 and detect subscriberrequests for service. Request for service indications are then providedto controller 612 for controlling the modem connections.

Each line interface and detection unit 610 is coupled to an associatedanalog/digital and digital/analog converter 614. Converters 614 are inturn connected to parallel/serial and serial/parallel converters 616.Converters 616 are coupled to a digital multiplexer 618 which operatesunder control of controller 612 to connect converters 616 to assignedmodems in modem pool 620. Modems in modem pool 620 are coupled to anetwork interface/multiplexer 622 and can be implemented using digitalsignal processors. As shown, network interface/multiplexer 622 iscoupled to and communicates with controller 612. This allows networkinterface/multiplexer 622 to know which modems and lines are activewithout having to monitor the communication traffic on the lines.

In operation, incoming communications are converted to digital words byconverters 614 and then converted to serial bit streams by converters.The serial bit streams are connected to an assigned modem by digitalmultiplexer 618. The modems in modem pool 620 then communicate withnetwork interface/multiplexer 622. For outgoing communications, theprocess is reversed. Serial bit streams from the modems are converted toparallel words and then to analog signals for transmission on data lines54. This digital switching implementation of communication server 58 canbe advantageous for switching of higher frequency XDSL communications.

FIG. 13A illustrates in more detail a frequency multiplexingimplementation for switching modem connections in communications server58. This frequency multiplexing implementation could be appropriate forbeing located at a cable operator as well as a central office of atelephone network. As shown, data lines 54 are coupled toreceiver/buffers 630 and transmit/buffers 632. Data off-hook detectors634 are coupled to the output of receiver/buffers 630 and providerequest for service indications to controller 636. For each data line54, communications server 58 includes a frequency agile modulator 638and a frequency agile demodulator 640. Each modulator 638 operates tomodulate an incoming analog signal at a selectable frequency. In theillustrated embodiment, the frequency is set to one of a plurality offrequencies, f1 to fN, equal in number to the number of availablemodems. Similarly, each demodulator 640 operates to demodulate at aselectable frequency where the frequency is set to one of the pluralityof frequencies, f1 to fN. Associated modulators 638 and demodulators 640are set to operate at the same frequency.

Modulators 638 provide signals to and demodulators 640 receive signalsfrom a mixer 642. Mixer 642 mixes the signals from modulators 638 andprovides the combined signal to demodulators 644. Each demodulator 644operates to demodulate the incoming signal at one of the frequencies, f1to fN, as designated by controller 636. Each demodulator 644 is coupledto and provides the demodulated signal to an associated modem 648 in themodem pool. By designating the appropriate frequency, controller 636effectively connects an assigned a modem 648 to a data line 54.

Outgoing signals are processed in an analogous manner. Each modem 648provides outgoing analog signals to an associated modulator 646designated to operate at the same frequency as the associateddemodulator 644. Modulators 646 modulate the analog signal and providethe modulated signal to mixer 642. Mixer 642 combines the modulatedsignals and provides the combined signal to each demodulator 640.Demodulators 640 demodulate the combined signal to recover theappropriate analog signal at their selected frequency and provide thedemodulated analog signal to transmit/buffers 632 for transmission. Inthis manner, modems 648 are connected to data lines 540 by modulatingand demodulating signals at one of the frequencies, f1 to fN.

FIG. 13B is a diagram of frequencies, f1 to fN, used in theimplementation of FIG. 13A. This results in each of the modems, m1 tomN, being assigned to one of the frequencies, f1 to fN, based upon thefrequency for the connected data line 54, as shown. In order to connecta data line 54 to a assigned modem 648, modulators 644 and demodulators646 are designated to operate at the frequency of the modulator 638 anddemodulator 640 for that data line 54.

FIG. 14A illustrates line interface modules (LIM) 650 and modem pool 652of a distributed switching implementation of communication server 58. Acontroller 653 is coupled to line interface modules 650 and to modempool 652. As shown, a plurality of line interface modules 650 arecoupled to the data lines and to modem pool 652. Each line interfacemodule 650 is operable to detect a request for service on the data linesand to connect each of the data lines it receives to each modem in modempool 652. Controller 653 operates to select a modem from modem pool 652in response to a detected request for service. Controller 653 thendirects the appropriate line interface module 650 to connect therequesting data line to the selected modem. In the illustratedimplementation, each line interface module 650 receives N data lines andincludes switches to connect the N data lines to any of the M modems inmodem pool 652. In this manner, the switching function is distributedacross line interface modules 650 and is scalable as support for moredata lines is added. In addition, although a two-wire interface isshown, the architecture of FIG. 14A can be used at a two-wire orfour-wire interface.

Line interface modules 650 allow switching capabilities to be scalablewith the desired number of modems and over-subscription. As an example,one implementation has four data lines connected to each line interfacemodule 650 and thirty-two modems in modem pool 652. For a 10:1over-subscription, this implementation would use 80 line interfacemodules 650 for connecting 320 data lines to the 32 modems in modem pool652. In order to double the number of supported data lines, another 80line interface modules 650 could be added along with another 32 modems.On the other hand, if a 5:1 over-subscription for 32 modems is desired,40 line interface modules 650 would be used to service 160 data lines.

FIG. 14B illustrates in more detail line interface modules 650 andmodems 660 in modem pool 652. As shown, each line interface module 650includes a plurality of line interface units 654 that receive one of theN tip and ring data lines. Each line interface device 654 includesmagnetics 656 and a plurality of switches 658. In the illustratedimplementation, magnetics 656 includes a transformer that receives tipand ring lines of the associated data line. As shown in FIG. 14B, a Tline is then provided to a plurality of switches 658 for connecting theT line to one of M outgoing lines. As shown, the M outgoing lines areequal in number to the number of modems 660 in modem pool 652. Thenoutputs of each line interface device 654 are connected together so thatline interface module 650 has one output line for each modem 660 inmodem pool 652 in addition to one output for the R lines. It should beunderstood that this can be implemented differentially using a pair ofswitches to switch the modem to the data line, rather than a singleswitch and a common R line, to enable switching R lines as well.

Modem pool 652 includes a plurality of modems 660 of which only thefront-end portion are shown. Each modem 660 receives two lines from lineinterface modules 650 using magnetics 662. Because of magnetics 656 andmagnetics 662, the switching and connections between line interfacedevices 654 and modems 660 are isolated from the data lines and from theback-end of modems 660. In one implementation, the connections betweenline interface modules 650 and modems 660 are accomplished on the backplane of a telecommunications chassis, and the line interface modules650 and modems 660 are implemented as cards that plug into the backplane. In this implementation, a controller communicates with lineinterface modules 650 and modems 660 to control switching connections tomodems 660.

Although the present invention has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the spirit and scope of the appended claims.

What is claimed is:
 1. A communication server, comprising: a pluralityof receiver/buffers coupled to associated data lines; a plurality offrequency agile modulators, each frequency agile modulator coupled to anassociated receiver/buffer, and each frequency agile modulator set tooperate at a unique frequency; a plurality of demodulators, eachdemodulator having a designatable operation frequency; a plurality ofmodems each coupled to an associated demodulator; a mixer coupled to theplurality of frequency agile modulators and coupled to the plurality ofdemodulators, the mixer operable to combine signals from the pluralityof frequency agile modulators and provide the combined signal to theplurality of demodulators; and a controller coupled to the plurality ofdemodulators, the controller operable to couple a selected data line toa selected modem by designating the demodulator associated with theselected modem to operate at the unique frequency of the frequency agilemodulator associated with the selected data line.
 2. The communicationserver of claim 1, wherein the communication server is located at acable system operator.
 3. The communication server of claim 1, whereinthe selected modem is an XDSL modem.
 4. The communication server ofclaim 1, wherein the selected data line is selected responsive to arequest for data service.
 5. The communication server of claim 1,wherein the data lines comprise twisted pair data lines.
 6. Acommunication server, comprising: a plurality of transmit/bufferscoupled to associated data lines; a plurality of frequency agiledemodulators, each frequency agile demodulator coupled to an associatedtransmit/buffer, and each frequency agile demodulator set to operate ata unique frequency; a plurality of modulators, each modulator having adesignatable operation frequency; a plurality of modems each coupled toan associated modulator; a mixer coupled to the plurality of frequencyagile demodulators and coupled to the plurality of modulators, the mixeroperable to combine signals from the plurality of modulators and providethe combined signal to the plurality of frequency agile demodulators;and a controller coupled to the plurality of modulators, the controlleroperable to couple a selected data line to a selected modem bydesignating the modulator associated with the selected modem to operateat the unique frequency of the frequency agile demodulator associatedwith the selected data line.
 7. The communication server of claim 6,wherein the communication server is located at a cable system operator.8. The communication server of claim 6, wherein the selected modem is anXDSL modem.
 9. The communication server of claim 6, wherein the selecteddata line is selected responsive to a request for data service.
 10. Thecommunication server of claim 6, wherein the data lines comprise twistedpair data lines.
 11. A method for coupling a plurality of data lines toa plurality of modems, the method comprising: modulating signalsreceived on a plurality of data lines at a unique frequency associatedwith each data line; mixing the modulated received signals to produce acombined incoming signal; and coupling a selected modem to a selecteddata line by setting the designated frequency of a demodulatorassociated with the modem to the unique frequency associated with theselected data line.
 12. The method of claim 11, wherein the method isimplemented at a cable system operator.
 13. The method of claim 11,wherein the selected modem is an XDSL modem.
 14. The method of claim 11,wherein the selected data line is selected responsive to a request fordata service.
 15. The method of claim 11, wherein the data linescomprise twisted pair data lines.
 16. A method for coupling a pluralityof data lines to a plurality of modems, the method comprising:modulating outgoing signals from a plurality of modems at differentdesignated frequencies; mixing the modulated outgoing signals from theplurality of modems to produce a combined outgoing signal; demodulatingthe combined outgoing signal at a unique frequency associated with eachdata line to recover signals for transmission on the data line; andcoupling a selected modem to a selected twisted pair data line bysetting the designated frequency associated with the selected modem tothe unique frequency associated with the selected data line.
 17. Themethod of claim 16, wherein the method is implemented at a cable systemoperator.
 18. The method of claim 16, wherein the selected modem is anXDSL modem.
 19. The method of claim 16, wherein the selected data lineis selected responsive to a request for data service.
 20. The method ofclaim 16, wherein the data lines comprise twisted pair data lines.